Sarcosine oxidase is an enzyme which catalyzes a reaction to oxidatively hydrolyze sarcosine to produce glycine, formaldehyde, and hydrogen peroxide. This enzyme can be used for determining creatinine or creatine levels in human sera or urine samples in combination with creatininase or creatinase and therefore is useful as a diagnostic enzyme for a variety of diseases such as hepatic disease.
Conventional sarcosine oxidases have drawbacks such as drastically decreased reactivity under neutral to weakly acidic conditions. Accordingly, they have generally been used under weakly alkaline conditions. See JP-B-1-34035, JP-A-5-115281, JP-A-8-238087, JP-A-6-113840, and JP-A-4-94688. However, when reacted with sera at the optimum pH range, those sarcosine oxidases react well with the substrate but are readily affected by bilirubin, causing errors in assay.
On the contrary, if sarcosine oxidase can be reacted with sera at a pH of approximately 6.5 it will not be affected by bilirubin and thus will not cause such errors. Accordingly, there has always been a need for a sarcosine oxidase which can be used under neutral to weakly acidic conditions.
Moreover, use of such enzyme with an increased reactivity under weakly alkaline conditions (i.e., lower Km value) will be very economical since a smaller amount of the enzyme can provide a sufficient reaction when used as a diagnostic enzyme under normal conditions.
An object of the invention is to provide sarcosine oxidase having a high reactivity under neutral conditions.
Another object of the invention is to provide a process for producing the sarcosine oxidase.